1. Technical Field
This invention relates to the art of radio broadcasting and, more particularly, to disconnecting and/or replacing one of a plurality of power amplifiers in a transmitter while the transmitter is operating.
2. Description of the Prior Art
The U.S. Pat. Nos. to H. I. Swanson 4,580,111 and 4,949,050 disclose an amplitude modulator for use in AM radio broadcasting and wherein the modulator serves to generate an amplitude modulated signal by selectively turning on and off a plurality of RF amplifiers in a digital manner to produce amplitude modulation. Each of the RF amplifiers provides an output voltage across the primary winding of a transformer. The secondary windings are connected together in a series circuit in a series combiner. Output current flows in the secondary windings to supply a load, such as an antenna for broadcasting an RF signal.
Frequently, such amplifiers are referred to as amplifier modules and such modules may be arranged side-by-side or stacked vertically. The modules are removably mounted in a cabinet so that each module may be removed for servicing or replacement. Before removal, the amplifier module is shut off but should not be removed until no current is flowing in the secondary windings. Normally, this requires that the transmitter be shut down. If such an amplifier module is turned off and an attempt is made to remove the amplifier from the series combiner, an open circuit will take place across the primary winding associated with the removed amplifier module. If the transmitter is still operating a high voltage potential will be developed across the open circuit of the primary winding and this will cause damage to the transformer and other associated circuitry. Consequently, the removal of such an amplifier module cannot take place while the transmitter is operating. The transmitter must be turned off before removing the amplifier module for repair. This creates discontinuity in the operation of the transmitter system.